For years, machines have been used to scan parcels as they move along a conveyor. Over-the-belt optical character recognition (OCR) systems have been recently developed that can capture an image of the surface of a parcel as it moves along a conveyor, and then create and process a representation of the image. The fundamental physical components of an OCR system are a sensor, an analog-to-digital (A/D) converter, and a computer comprising a central processing unit (CPU) and a memory. The individual physical components of an OCR system are all well known in the art, and many alternative embodiments of each of the individual physical components are commercially available, with differing cost and performance characteristics. Much effort goes into finding the most efficient combinations of components for particular applications, and in the development of computer software programs that process the images created by these familiar physical components.
Charge-coupled device (CCD) sensor arrays are often used in OCR systems. A CCD camera consists of an array of electronic "pixels," each of which stores an accumulated charge according to the amount of light that strikes the pixel. A CCD camera is used to quickly capture an image of the surface of a parcel as it moves along a conveyor. The image is converted into digital format which may be stored as a bit map in a computer memory. The CCD array is then cleared as the charge within each pixel is read, and the array is ready to capture the image of another parcel or section of a parcel. In this manner, a single CCD camera is used to scan a great many parcels.
Computers that may be used to process the images captured by CCD cameras vary in computation speed and other parameters. Generally, a faster computer is more expensive than a slower computer, a computer with a large memory capacity is more expensive than a computer with a smaller memory capacity, and a special purpose computer is more expensive than a general purpose computer. There is therefore a financial motivation to use low speed, low memory, general purpose computers whenever such are suitable for a particular purpose.
Parcel delivery companies, such as United Parcel Service (UPS), could make extensive use of OCR reader systems. UPS ships millions of parcels every day. If OCR systems were used by parcel delivery companies such as UPS they would generate an enormous amount of computer data. There is therefore a need to limit the amount of image data that must be saved for processing by a text reader. There is also a need for computer systems that can quickly and accurately process the images created by CCD cameras. For example, computer systems have been developed that can attempt to read the destination address written on certain parcels, so that the parcels may be correctly routed to their destinations when the address is successfully read. Reading text is a sophisticated task, and a system capable of doing so is commensurately sophisticated and may comprise expensive equipment such as a high resolution CCD camera and a high speed, storage, and processing, or special purpose computer.
To the extent that less expensive equipment can perform less sophisticated tasks in an OCR system, more expensive equipment can be dedicated to reading text. Determining the location and orientation of the destination address on a package moving along a conveyor is an example of a function required of an OCR system that has been performed with sophisticated equipment than that is also used to read text. There is therefore a need for a system using low cost equipment such as a low resolution CCD camera and a general purpose computer to determine the location and orientation of the destination address on a package moving along a conveyor.
Miette, U.S. Pat. No. 5,103,489, describes a label, and a method and device for locating addresses on mailed articles to be sorted. The system uses a preprinted mailing label including an address locating mark located in a known relation to the area on the label where the destination address is likely to be written. The address locating mark is a black ink circle including a rotation specific image inside the circle. A space for the destination address is included on the label to the side and below the mark. The surface of the package is imaged with a single camera system, and the location and orientation of the mark is ascertained. The destination address is then read in the expected area, and at the expected orientation, with reference to the location and orientation of the detected mark.
The system described by Miette reduces the amount of data that must be processed by the text reader. The address locating mark is located on a mailed article in a known relationship to the position and orientation of the destination address. The text reader may then process only the data within a relatively small area and at an orientation defined with respect to the mark. The system described by Miette is used to scan closely arranged items such as magazines exiting an unstacking device. In such a system, the items to be scanned are of uniform size and shape, and little time elapses between consecutive items. Moreover, the entire surface of every item must be searched for the mailing label. Therefore, Miette is not concerned with limiting the amount of high resolution CCD camera data that must be stored for subsequent processing.
The single camera system described by Miette would have a significant disadvantage if applied to parcels moving along a conveyor because the address locating mark could not be used to limit the amount of CCD camera data that must be stored in a computer memory for processing by the text reader. A high resolution CCD camera scanning a moving conveyor, such as one suitable for use with a text reader, generates a tremendous amount of data. Most of the data is a useless image of the conveyor and the non-text bearing areas of the parcels moving along the conveyor; only a small percentage of the data includes the important destination address bearing portions of the parcels. The single camera system described by Miette would require storing all of the data generated by the high resolution CCD camera even though only a small portion of the data would be processed by a text reader. The system described by Miette also relies on preprinted address labels. It would be advantageous if an OCR system for a parcel handling system was not limited to reading addresses written on preprinted labels.
Kizu et al., U.S. Pat. No. 4,516,265, describes a two camera system that reads the postal (zip) codes on envelopes traveling on an envelope transport system. The two camera system includes a low resolution pre-scanner that coarsely scans the surface of the envelope. The position of the destination address block is determined from the coarse scan, and the coordinates of the destination address block with respect to the leading edge of the envelope are then passed to a second camera system. The second camera system scans the destination address block by first detecting the leading edge of the envelope. The second camera then starts scanning when the destination address block reaches the second camera and stops scanning when the destination address block moves past the second camera. A postal code reader then processes the high resolution scan and detects and reads the postal code.
The two camera system described by Kizu et al. does not use an address locating mark to determine the position and orientation of the destination address block on a letter. Rather, Kizu et al. relies on the positional relation and sizes of the indicia bearing areas (i.e., stamp and post mark, destination address block, and return address block) on the envelope. The position and size of the destination address block is then defined with respect to the leading edge of the envelope. The timing of the operation of the high resolution camera is then controlled to limit the amount of the surface of the envelope that is scanned with the high resolution camera. Thus, Kizu et al. relies on the envelope, and the destination address on the envelope, being properly oriented on the envelope transport system. Kizu et aL also relies on the envelope having a well defined leading edge.
The two camera system described by Kizu et al. would therefore not be suitable for an over-the-belt OCR system for arbitrarily positioned parcels bearing arbitrarily positioned destination address labels moving along a conveyor. The system described by Kizu et al. cannot ascertain the position and orientation of the destination address blocks on parcels with arbitrarily positioned destination address labels, such as those conveyed in a parcel handling system. Similarly, the system described by Kizu et aL does not have a method for reading the destination address on a parcel that does not have a well defined leading edge, such as a parcel with soft or irregular edges.
Therefore, after Miette and Kizu et al. there remains a need for an OCR system which minimizes the amount of high resolution CCD camera data that must be stored for processing by a text reader. There also remains a need for a two camera OCR system that can ascertain the orientation of arbitrarily positioned destination blocks on articles moving along a conveyor, such as those conveyed in a parcel handling system. There also remains a need for a two camera OCR system that can read information on a parcel that does not have a well defined leading edge.